import numpy as np
import cv2 as cv
# Create a white image
img =np.ones((512,512,3),np.uint8)*255
startPt=(0,0)
endPt=(round(img.shape[1]/2),round(img.shape[0]/4))
color=(0,255,0)
thinknessPx=3
cv.rectangle(img,startPt,endPt, color,thinknessPx)
cv.imshow("img", img)
cv.waitKey()
cv.destroyAllWindows()